(1) Field of the Invention
The present invention relates to enhancing the realism with which the sounds produced by musical instruments are electronically simulated and particularly to a technique wherein the transition from either the attack or sustain portion of a waveform commensurate with a selected sound to the release portion of the waveform may be accomplished smoothly and virtually at any time. More specifically, this invention is directed to a signal generator circuit for use in an electronic musical instrument and especially to an improved circuit for controlling the reading of memorized signals commensurate with the various periods of notes produced by actual musical instruments. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
Hereinafter, individual sections or periods of a waveform commensurate with a note played on a musical instrument will be referred to using the conventional terminology, i.e., "attack", "sustain", and "release".
The state-of-the-art prior to the present invention is believed to be exemplified by the disclosure of Published German Patent Application No. 27 15 510 which claims priority from Japanese Application P No. 51 38466. Thus, as disclosed in German Application No. 27 15 510, if a percussion sound is to be simulated, for example a sound as produced by a piano key striking a string, a complete waveform will be memorized including attack, sustain and release sections. Thereafter, if the note is to be electronically simulated, a key on a manual (keyboard) of the electronic musical instrument will be depressed whereupon the memorized waveform is read completely even if the player prematurely releases the key. However, in accordance with the prior technique, should the key be released prior to recreation of the entire memorized note, the waveform will be modified. Specifically, the data read-out of the memory after release of the key will be multiplied by an attenuation function.
If it is necessary for the electronic musical instrument to produce sounds having a sustain portion of the waveform which is of arbitrary duration, as would be required to simulate an organ, it is suggested in German Application No. 27 15 510 that the data commensurate with the sustain portion of the waveform be attenuated, quickly or slowly as required, and this attenuated sustain data be utilized as the release portion of the note.
The prior art technique, as briefly described above, has two major disadvantages. Firstly, the sound produced has a somewhat unnatural quality. Secondly, implementation of the prior technique requires a comparatively large data storage capability.